Electrostatic precipitator and air conditioning system incorporating the same



Jan. 22, 1957 R. A. YEREANCE 2,778,443

ELECTROSTATIC PRECIPITATOR AND AIR CONDITIONING SYSTEM INCORPORATING THE SAME Filed April 5. 1954 2 Shegts-Sheet 1 INVENTOR. 959d. .5: P052997 A. VFQEAIYCA' BY WM QWL 1957 R. A. YEREANCE 2,

ELECTROSTATIC PRECIPITATOR AND AIR CONDITIONING SYSTEM INCORPORATING THE SAME Filed April 5, 1954 2 Sheets-Sheet 2 INVENTOR. 205527 A. JQ-IQEAAKE A rive/V6115 United States Patent ELECTROSTATIC PRECIPITATOR AND AIRCON- ISHTIONING SYSTEM INCORPORATING. THE

Robert A. Yereance, Seattle, Wash., assignor to Boeing Airplane Company, Seattle, Wash., a corporation of Delaware Application April 5, 1954, Serial No.'420,888

12 Claims. (Cl. 183-7) Usually this direct voltage source included one or more high-voltage transformers and one or more high-voltage rectifiers with associated apparatus, which together added greatly to the expense and to the weight and bulk of the precipitator apparatus. For many applications, such as residential forced air heating systems and-air conditioning systems, the factors of initial cost and maintenance cost of such electrostatic precipitator apparatus render the same unfeasible from the economic standpoint.

stance, the factors of weight and bulk render such precipitator apparatus impractical.

A general object of the present invention is an efiective self-charging electrostatic precipitator apparatus, that is an apparatus which generates its own high voltages and requires no external high-voltage supply, in order to produce the necessary high-gradient electrostatic fields therein.

A related object of the invention is an electrostatic precipitator which may be manufactured in lightweight, compact and relatively inexpensive forms and which will be as eifective or more so for its intended purpose as much more expensive, heavy, bulky and troublesome devices requiring electronic, or other high-voltage supply sources.

A more specific object of the invention is an effective In the case of air conditioning systems for airplanes, for in-.

electrostatic precipitator of the self-charging type wherein I very high voltages are obtainable and correspondingly effective separation of liquid droplets and solid particles from the gaseous medium which is passed through the apparatus.

Still another object is an electrostatic precipitator'haw Another important object of the invention is an efiec- 1 tive electrostatic precipitator of the self-charging type' which may be made in a form producing relatively slight or negligible resistance to flow of gaseous medium through the apparatus passages. A related object is an air conditioning system incorporating electrostatic precipitator means capable of acting effectively to remove excessive moisture and foreign particles in'zthe'air being' processed without serious reduction of air velocity in the ice forced air passage of the system in which such precipitator means is incorporated.

In accordance with the invention, a gaseous suspension requiring processing for precipitation of solid or liquid particles contained'therein is passed through two similar precipitator units having certain electrical interconnections, as hereinafter described, which produce the selfcharging efiect. sion first passes through a grounding zone wherein the liquid or solid particles to be separated are relieved of' charge. The particles now neutralized are next carried past an insulated priming electrode, maintained at high. potential of one polarity in accordance with the self charging operation of the combined apparatus as herein- 1 after more fully described, and in the process of so doing, such particles receive a charge of the opposite polarity. The gas stream now divides and some of these charged particles aredirected into electrical contact with an interior surface of an insulated electrodecondenser element to which they give up their charge, and the remainder of f these charged particles, representing most of the particles: carried by the incident gas stream, are directed through; a space defined by an exterior surface of said electrodecondenser element and a grounded conductive surface: of a particle-collector element facingsaid exterior surface: from a distance. The'high potential imparted to the exterior surface of the electrode-condenser elementas a result of that elements accumulation of charge from the impinging charged particles serves two important purposes in each unit of the precipitator apparatus. It is applied by an electrical connection to the priming electrode of the other precipitator unit, and it sets up an electrostatic field in the adjoining space, defined above,

which repels said remainder of charged particles into impingement on the grounded particle-collector element. There they collect and remain or are drawn off by suitable apparatus. Thus, in the process of flowing through the two precipitator units of the apparatus, suspended particles to be separated from the gaseous medium cause an exchange of electrical charge to take place, asbetween the priming electrode elements and the electrode 'condenser elements of the respective units, giving rise-to the development of very high voltages producing the abovedescrib'edseparating action.

The self-charging action of the precipitator apparatus is self-starting inasmuch as the cross-connected priming electrode and electrode-condenser elements of the respective precipitator units constitute a basically unstable charge transference system, which is bound to be triggered into building up one condition of substantially stable charge equilibrium or the opposite condition, depending upon any initial differential average charge carried by particles impinging the respective electrode-condenser elements at an initial instant when the system is conditioned for operation.

In the preferred embodiment of the invention, the two precipitator units of the apparatus are arranged in parallel, i. e. interposed in parallel branches of the air conditioning system or other system in which the invention is embodied. The priming electrodes and the electrodecondenser elements are preferably of tubular form, Whereas the particle-collector elements are also of tubular form and constitute a section of the branch duct wall surrounding the electrode-condenser tubes.

The grounding zone through which the particles first pass in each unit of the precipitator apparatus may be established in any of several Ways, certain preferred ones of which are illustrated and described hereinafter. Such zone may be established by a'fine-mesh wire grid placed at ground potential and arr-anged so that the particles carried by the stream of airor other gas must pass Patented Jan. 22,

In each such unit the gaseous suspen amassthrough the mesh openings in close proximity to a grid wire, giving up their charge to such wires in so doing. A second arrangement for establishing the grounding zone is to provide an, electrical, resistance wire screen subset-am tially grounded and heated to veryhigh temperature by passage of electric current therethrough, in order. to pro duce an electrically conductive atmosphere generally in the plane of the grid through which the particles must pass, so that such particles will loose charge and become neutralized in so doing. Still another arrangement generally similar to the arrangement just described, in that the, gas is rendered conductive in the grounding zone, is the provision of'a grounded source of radiation of very short Wave lengths, such as that provided by most radioactive substances, which will ionize the atmosphere so that passage of the suspended particles through this ionized zone willcause such particles to lose charge.

These and other features, objects and advantages of the invention will become more fully evident from the following description by reference to the accompanying drawings.

Figure l is a simplified and partly schematic sectional diagram of a portion of an air conditioning system, incorporating the improved electrostatic precipitator in which the electrically interconnected units are in a parallelduct arrangement.

Figure 2 is a similar view at a larger scale showing one of the branches, or precipitator units, in the system of Figure 1.

Figure 3 is a perspective view of an electrical resistance wire grid structure which may be used for creating the grounding zone employed in the entrance to each unit.

Figure 4 is a perspective view of a radioactive device for creating the grounding zone.

Figure 5 is a simplified. and partly schematic sectional view of a modified form of the electrostatic precipitator apparatus in a duct of an air conditioning system.

Referring to Figures 1 and2, the air conditioning system embodying the present invention in. one form con1- prises a main duct or condui-tld; through which air is passed containing droplets or particles of liquid to. be precipitated out of suspension in the air, together with particles of dust or other-solids,,iif any, likewise topbe separated from the air. it is assumed, in the illustrated case that the accumulation of precipitated w-ater'droplets on the collector surfaces of the apparatus will be sufiicicnt to hold precipitated solid particles impinging the same surfaces, and to carry out these particleswitln the removal of suchwater-during continued operationofthe apparatus. lit will be understood by those skilled in the art, however, that films of oil or other-tacky substances may be used on collector surfaces in the apparatus for holding precipitated solid particles in the event theamount of precipitated water droplets is insufilcient for that purpose. In the primary application for which thepresent invention was originally developed, namely, air conditioning systemsin airplanes, the problem of, separating water particles entrained in the ventilating air supply was. the principal problem, and the separation ofdust, and other solid particles was incidental. For purposes of the in vention, the air duct is divided into left and right branches 10L and WK, respectively, in any suitable manner or physical arrangement depending upon the various factors which affect design convenience and economy. With the arrangement of precipitator unit components shown in Figures 1 and 2, it is necessary that the air to be processed be passed through the branch ducts in the direction of the arrow, namely, from the top toWard-thebottom of the'figure.

The particle-laden air flowing downwardly in the branchduct 10L and into the precipitator unit 12 incorporated in that branch duct, first, passes through the openings of a fine-mesh screen 14which is grounded-by means of electrical contact of the edges ofsuch screen with the groundedwallsof themetallduct 10L. this screen, the entrained particles of water and solids are In p si g hrough;

e d, o harg s, s nce he. me h. p nin s in he s r en are made so small that the particles must pass in very close proximity to a screen wire in order to pass through the plane of the screen. in effect therefore, the screen i4 establishes a grounding zone in which the particles are .eutralized of electric charge as they fiow into the precipitator unit 12. Other arrangements for providing the grounding zone, appear in Figures 3 and 4-, respectively. In Figure 3 the grounding zone is established by means of a grid formed of electrical resistance wire 16.carried by ceramic supporting ring 18 which is mounted in the entrance of precipit-ator unit 12. Electric current is passed through the resistance wire 16 to heat the wire to a very high temperature (near incandescence) so that the air in the vicinity of the grid wire elements becomes conductive to a substantial degree. Since one end of the electrical resistance wire grid is grounded, as at 16A, and. its oppositev end is connected to a source of heating current at a potential, not high above, ground (such as a conventional11.0v volt A. C. supply) particles passing through the general plane of, the grid are relieved of charge. Theyadyantase of the arrangement in Figure 3 over that in Figures 1 and 2 is that the desired charge neutralization is accomplished without appreciable resistance to the. flow of air through the grid. In this regard it will be evident that the spacing between the grid wires may be much greater in the case of Figure 3 than in the case ofFigures l and 2 because of the conductivity of the, air createdinfthe arrangement of Figure 3.

In the modified, arrangement of Figure 4 the grounding zone is established by radiation from radioactive substance embodied in. slugs, or cartridges 20 embedded in the base of the annular groove formed around the inside of the lead ring 22, The depth and width of the groove inside the ring 22; are such that a narrow beam of radiant energy is directed, across the space contained within the ringandthe radioactive particles from one radiating unit 20, are safely intercepted by the mass of lead in the oppositely situated wall of the ring. In this arrangement, no, physical obstruction to the flow of air through the grounding zone. isv presented since conductivity or ionization of air within the region surrounded by'the ring 22causes particles of moisture and solid mat: terfl'owing; transversely'through the ring opening to be relieved; of charge or to assume substantially the potential' of; the ring 223136112, which in this case is placed at ground potential by virtue of an electrical connection to the surrounding walls of the branch duct 10L.

Following their passage through the grounding zone, the entrained particles enter the electrostatic field created= by thepriming-electrode 24, representing a section of metallic branch duct tubing which is electrically insulated from the branch duct tubing above it by reason of the interposed tubular section of insulating material 26, andfrom the metallic tubing below'it by reason of the interposed tubular section of insulating material as. The priming/electrode 24: is maintained at a highpotential of onepolarityi (negative-polarityin the illustration) and particles-Which enter thefield of this priming electrode therefore become charged positively by electrostatic induction.- 'IJhe; mannerin which the priming electrode zd becomes, highly chargedin.thefirst-instance will be describedhereinafteri The entrained. particles now charged. positively by virtue of their passage from the grounding zone toward and through the negatively charged priming electrode 24 enter a chamber formed'by. the enlarged duct section 3t), wherein some of theseparticles, because of their momentum in the-moving air stream, pass into thethroat of the metallic tubular member 32 mounted by insulating supports'34'. generally centrally'and coaxially within the enlargediduct sectiona30t Themetallic tubular member 32; insulated fromthe conducting wallsof the duct sectiom3ll; comprises anielectrode-condenserelement. The positively chargecli'lJttrlicrles.whichv enter the interior of this metallic element are deflected outwardly by the conical baffle 36 into impingement with the inside Surface of the element, where they give up their charge to the element itself. Other suitable means to intercept the positively charged particles could be mounted inside the tubular electrode-condenser element 32 in order to relieve these particles'of charge and conduct the charge to the 6 tials on these two elements. Thus, during the instant in question the, element 32 may be charged more positively than the element 46, or vice versa. This action takes place due to the inevitable generation of electrical element 32" so as to provide a cumulative positive charge on the element. itself. shell, such as the tubular element 32, will not sustain an electrostatic field, it will be apparent that the cumulative charge imparted by the impingement of particles on the inside wall of the electrode-condenser element flows to the exterior surface of this element, so that in the stable condition of operation of the precipitator apparatus there will be a high potential established on the exterior surface of the electrode-condenser element 32. In the example this potential is positive, and it serves two purposes. First, it serves to place the electrode-condenser element 38 of the second precipitator unit 40 at an equal high potential by means of the electrical connection 42 between the priming electrode 38 and'the electrode-condenser element 32. A similar electrical connection 44 exists between the priming electrode element 24 of the unit 12 and the electrode-condenser element 46 of the unit 40.

The section of tubing 30 is grounded, as at 48. Consequently, an electrostatic field of high voltage gradient is set up in the annular space surrounding the highly charged electrode-condenser element 32. The remaining positively charged particles which enter the chamber defined by enlarged tubular section 30 and which do not enter the interior of electrode-condenser element 32 are repelled outwardly by the positive charge on the latter and into impingement with the inside walls of the grounded tubing section 30. The second purpose of the positive charge developed on the exterior of element 32 is thus to deflect the positively charged particles so that they will precipitate on the chamber walls represented by the interior of the conductive tubing 30. In case these particles are water, they are relieved of charge upon striking the wall of tubing 30, collect and run down the walls to a collecting trough 50, which is drained through discharge tubes 52 through small holes in the wall of tub- Since the interior of a metallic ing section 30. A similar collecting trough 54 is formed around the inside of the electrode-condenser tube 32 such that particles precipitated within this tube are likewise retained. Drainage from the collecting trough 54 takes place through the tubular insulating supports 34 charges on particles suspended in moving air. There are various explanations and difierent possible reasons as to why particles suspended in moving air take on electric charge even in the absence of a surrounding electrostatic field capable of inducing that charge in the particles. Thus, the particles may receive a charge as a result of friction between air particles, by reason of the splitting of the particles themselves caused by air turbulence, by reason of the particles themselves striking part of the mechanical structure in the system or because of other natural phenomena. In any event, the instant the air conditioning system is placed into operation and air is passed through the main conduit 10 in the direction shown by the arrows, one of the electrode-condenser elements will immediately receive an instantaneous positive charge, or a more positive charge than the other such element, and the potential of this charge will be applied to the priming electrode of the opposing precipitator unit. In the example the electrode-condenser element 32 is assumed to receive the more positive charge, in which case entrained particlesvpassing into the resulting field of the priming electrode 38 have induced in them a negative charge, which results in a transference of negative charge to the electrode-condenser element 46. The negative charge on the latter applies negative potential to the opposing priming electrode 24 through the cross-connection 44. Thus, entrained particles passing into the field of the priming electrode 24 receive a definite positive charge by electrostatic induction and add to the positive chargeinitially existing on the electrode-condenser element 32. This, in turn, increases the negative charge on the electrode-condenser element 46. Thus, due to the positive feed-back efl'ect existing in the system the positive charge developed on one electrode-condenser element contributes to the negative charge developing on the other electrode-condenser element and the latter, in turn, further increases the positive charge on the former element, the process being cumulative to build up very high voltages in the precipitator apparatus. Stable equilibrium is reached, that is, the process of charge increase ceases when the electrostatic fields surrounding the electrode-condenser elements have such a high repelling efiect on charged particles flowing toward these elements that only a sutficient number of these particles by which the element 32 is centrally mounted within the tubing section 30, as shown.

In case the precipitated particles are solid matter, they will of course be caught by the condensed moisture inside the walls of tubing section 30 and condenser element 32 and will be washed down those walls and out the drains for the respective collecting troughs and 54.

The details of construction and operation of the precipator unit 40 are similar to those of precipitator unit 12 already described.

In the operation of the combined precipitator apparatus,'including the two similar precipitator units 12 and 40, it may be assumed that at the outset no charge exists on any of the priming electrodes or electrode-condenser elements in the apparatus. Under these conditions the electrical system comprising these elements and the crossconnections 42 and 44 placing the priming electrodes 24 and 38 of the precipitator units at the respective potentials of the electro-condenser elements 46 and 32 of the opposing units has an unstable equilibrium. When air containing particles to be separated is passed through the two branch ducts under the assumed condition of no charge on such elements, there will inevitably be an unbalance in the average charge carried by particles entering the respective electrode-condenser elements 32 and 46 at any given instant of time, which unbalance will be reflected in an instantaneous unbalance of the potenare permitted to enter the interiors of the respective electrode-condenser elements in order to maintain the existing level of charge thereon. In other words, there is an automatic saturation condition in which the number of particles entering the electrode-condenser elements 32 and 46 are sufficient to offset the continuing loss of charge due to leakage effects, corona, etc. The voltages permitted in the apparatus before saturation takes place will depend upon the physical design and arrangement of the components. Highly eifective precipitator action may be achieved with a' very simple apparatus arrangement such as that illustrated, wherein the requisite highgradient electrostatic fields are generated by self-charging action and without necessity of any external voltage supply, such as in previous electrostatic precipitator apparatus.

In the modified arrangement shown in Figure 5, the components of each of the precipitator units 12' and 40' may be similar to those of the precipitator units described in the case of Figure 1. The difierence between the two embodiments lies not in the details of the individual precipitator unit, therefore, but in the arrangement of these units, which in this instance are disposed in series arrangement so that no branching of the main 'air duct 10 is necessary in order to incorporate the preare shown in the drawings. for draining .ofi the precipit'ated' water and solid particles; however, it will be understood that arrangements similar to those employed in the preceding form may also be used in this case.

In the operation of the embodiment shown in Figure 5, it is assumed that air passing through the upper precipitator unit 12" is not entirely relieved therein of particles to be precipitated from the air, so that the air which flows through the lower unit 40' after it leaves the upper unit still has in it a. substantial quantity of particles to be precipitated out. Any residual charge carried by these particles flowing out of the lower end of the upper unit 12 is removed therefrom asthey pass through the grounding zoneestablished by the grid 56 at the entrance of the lower unit 49. Thus, the conditions for self-charging operation involving charged transference in an electricalsystem havihgan initial unstable equilibrium asin the first-described form are also present in the form illustratedin Figure 5. The positive charge which initially develops on one of the electrode-condenser elements is thereby caused to contribute to the negative charge developed on the other electrode-condenser element, which in turn further contributes to the positive charge on the first element, etc.

The terms grounded, ground potential and like terms as used herein are intended to refer to a potential which represents true ground potential or a fixed potential. In this regard it will be appreciated that true grounding of elements which are referred to as grounded is usually the most convenient way of securing a ground potential effect. This applies both to the grounding zone devices and to the enlargedtubing sections surrounding the electrode-condenser elements. However, since the operation of the apparatus depends only onrelative potentials it is possible to use any practicable fixed potential as ground potential within the meaning of that term as used herein.

These and other variations of the invention will be apparent to those skilled in the art.

i claim as my invention:

1. Electrostatic precipitator apparatus comprising a pair of precipitator units, means to pass through said units a gaseous medium containing particles to be separated from said medium by said precipitator apparatus, each of said units comprising an inlet passage for the gaseous medium, an outlet passage for the gaseous medium, means creating a grounding zone for relieving the particles of charge which entered through said inlet passage, insulated conductive means forming a priming electrode maintained at high potential of one polarity and arranged to be passed by the moving particles following their passage through said grounding zone, thereby to induce in such particles a charge of opposite polarity, insulated conductive means forming an electrode condenser element having on one side a surface impinged by some of said charged particles to receive charge therefrom and on its opposite side an electrode surface sustaining a high polential established by the. accumulated charge, means including said electrode surface and a grounded conductor spaced therefrom defining a passage for the gaseous medium carrying the remainder of the charged particles and leading to said outlet passage, whereby said latter particles are repelled from said high-potential electrode surface to said grounded conductor for collection on the latter, and means electrically interconnecting the priming electrode of each such unit with the electrodecondenser of the other such unit.

2. The electrostatic precipitator apparatus defined in claim I wherein the electrode-condenser element of each unit comprises tubular conductive member the inside surface or" which comprises the surface impinged by the charged particles andthe outsidesurface of which comprises the electrode surface thereof.

3. An air conditioning systemcomprisiugin combination a duct through which is passedthe air containing particles of matter to be separated from. such air, a

pair. of precipitator units, means to conduct air from saidv duct into and through said precipitator units, duct means for conducting away the air discharged from said precipitator units, said precipitator units individually comprising an inlet passage for the air to be processed, an

outlet passage for discharging the air into said duct means,

high potential established by the accumulated charge,

means including said electrode surface and a grounded conductor spaced therefrom defining a passage for the air carrying the remainder of. the charged particles, whereby said latter particlesxare. repelled fromsaid highpotential electrode surface to said grounded conductor for collection. on the latter, and means electrically interconnecting the-priming electrode of each such unit with the electrode-condenser element of the other such unit.

4. The air conditioning system defined in claim 3, wherein the means to conduct air to the precipitator units comprises a; pair of ducts branching from the first-mentioned duct, and wherein the duct means to carry away the. air discharged from the precipitator units comprises converging branch ducts leading into the last-mentioned duct, whereby the air to. be. processed is divided so that part. flows through one precipitator unit and the remainder through the other precipitator unit.

5. The air conditioning. system defined in claim 3, wherein the precipitator units are in series arrangement, the inlet for onev such unit being connected directly to the first-mentioned. duct, the outlet of such unit being connected to the inlet. of the second unit. and' the outlet of the latter unit being connected to. the last-mentioned duct for carrying away the processed air.

6. The air conditioningv system defined in claim 3, wherein the electrode-condenser element of each. unit comprises a tubular conductive. member the inside surface of which comprises the surface impinged by the.

means creating a groundingzone forrelieving the particles of charge which enter through said inletpassage, insulated conductive means forminga priming electrode maintained athighpotentialof one polarity and arranged tobe passed by the moving particles.following their passage through said grounding zone, thereby to induce in-such particles a charge ofopposite polarity, insulated conductive meansv forming an electrode-condenser. element of hollow formv havingan inside surface. impinged by some of said'charged particles to receive charge therefrom and having .an outside surface constituting an electrode sustaining a high potential established by the accumulated'charge on said electrode-condenser element, means including said electrode-condenser element defining a passage forthe'gaseous medium extending along the exterior surfaceof said electode-condenser element for conducting the gaseous medium carrying the remainder of said charged particles, whereby said latter particles are repelled'from'said highpotential electrode surface, and a grounded" element ad joining said last-mentioned'passage and'facing said electrode-condenser element to be impinged by the repelled charged particles, means for removing the charged particles impinging on said grounded element, and means electrically interconnecting the priming electrode of each such unit with the electrode-condenser element of the other such unit.

8. Electrostatic apparatus comprising a pair of precipitator units, means to pass through said units a gaseous medium containing particles to be separated from said medium by said apparatus, each of said units comprising an inlet passage for the gaseous medium, an outlet passage for the gaseous medium, means creating a grounding zone for relieving the particles of charge which entered through said inlet passage, said grounding zone means comprising means producing an ionized atmosphere in said grounding zone, said means being grounded and thereby removing charge from particles passing through said grounding zone, insulated conductive means forming a priming electrode maintained at high potential of one polarity and arranged to be passed by the moving particles following their passage through said grounding zone, thereby to induce in such particles a charge of opposite polarity, insulated conductive means forming an electrode-condenser element having on one side a surface impinged by some of said charged particles to receive charge therefrom and on its opposite side an electrode surface sustaining a high potential established by the accumulated charge, means including said electrode surface and a grounded conductor spaced therefrom defining a passage for the gaseous medium carrying the remainder of the charged particles and leading to said outlet passage, whereby said latter particles are repelled from said high-potential electrode surface to said grounded conductor for collection on the latter, and means electrically interconnecting the priming electrode of each such unit with the electrode condenser of the other such unit.

9. Electrostatic apparatus as defined in claim 8, wherein the ionizing means comprises a charge of radioactive substance and means supporting said charge to direct its radiation generally transversely to the path of movement of the gaseous medium.

10. Electrostatic apparatus as defined in claim 8, wherein the ionizing means comprises a grid of electrical resistance wire extending transversely across the path of movement of the gaseous medium and arranged to be heated by passage of electric current through said grid to a temperature producing ionization of the gaseous medium in the vicinity of the grid wires.

11. Self-charging electrostatic precipitator apparatus comprising a pair ofprecipitator units, means to pass through said units gaseous medium containing particles to he precipitated from such medium, said precipitator units individually comprising an inlet and outlet, means stationed along the path of said medium placing said particles at ground potential, priming electrode means stationed next along the path of said medium inducing a particles and collect the charge therefrom for transference by electrical conduction to said exposed surface, and grounded particle-collecting means spaced from said exposed surface to define a passage therebetween for the gaseous medium carrying the remainder of the charged particles toward said outlet, whereby the potential of said posed surface produced by the accumulated charge on said electrically conductive device repels said remaining particles toward said collecting means, and means electrically connecting said electrically conductive device of each unit to the priming electrode of the other unit for producing cumulative increase of charge in said units.

12. Self-charging electrostatic precipitator apparatus comprising a precipitator unit, means to pass through said unit gaseous medium containing particles to be precipitated from such medium, said precipitator unit comprising an inlet and outlet, means stationed along the path of said medium placing said particles at ground potential, priming electrode means stationed next along the path of said medium inducing a charge in said particles of one polarity, means stationed next along the path of said medium and including an electrically conductive device having an exposed surface and an electrostatically shielded surface, said latter surface being disposed to intercept some of said charged particles and collect the charge therefrom for transference by electrical conduction to said exposed surface, and grounded particle-collecting means spaced from said exposed surface to define a passage therebetween for the gaseous medium carrying the remainder of the charged particles toward said outlet, whereby the potential of said exposed surface produced by the accumulated charge on said electrically conductive device repels said remaining particles toward said collecting means, means electrically connected to said electrically conductive device and automatically converting the potential thereof into a potential of opposite polarity, and means applying such latter potential of opposite polarity to said priming electrode, thereby to produce increased charge on said electrically conductive device.

References Cited in the file of this patent UNITED STATES PATENTS Jacob Aug. 7, 1945 Fruth Apr. 22, 1952 OTHER REFERENCES 

